Northstar Engines and System Technical Discussion Discussion, Tappets or Rocker Followers - Two Different Head Designs??? in Cadillac Engine Discussion; I'm currently fighting a nasty knocking sound on my Northstar powered Lucerne CXS and I've been looking at heads on ...

Tappets or Rocker Followers - Two Different Head Designs???

I'm currently fighting a nasty knocking sound on my Northstar powered Lucerne CXS and I've been looking at heads on eBay. It seems there are two varieties of heads for the Northstar... those with tappets where the cam is in direct contact with the tappet and those with rocker followers where the cam is actuating a follower with a roller tip. Can anyone explain the difference and which vehicles/variants of the northstar used which type of head configuration? I see a lot of confusion in the forums regarding the language and terminology. My Lucerne shop manual describes the heads as though I have rocker followers but when I pulled the valve covers my Northstar has tappets. With the tappet configuration there are no visible valve springs. Did someone do a motor swap on my Lucerne before I bought it or is the factory shop manual just wrong?

Re: Tappets or Rocker Followers - Two Different Head Designs???

00+ motors have the roller tip lifters. Pre 00 motors have the lifter buckets. The lifter buckets unfortunately can wear in the center of the bucket from contact with the cam. The roller tip lifter, rides over the cam lobe.

With the lifter buckets, the valve spring will not be visible. It's under the lifter bucket which sits on top of the valve tip.

What year Lucerne do you have?

Hopefully you haven't had the bait and switch routine pulled on you....

Re: Tappets or Rocker Followers - Two Different Head Designs???

Originally Posted by pcmos

I'm currently fighting a nasty knocking sound on my Northstar powered Lucerne CXS and I've been looking at heads on eBay. It seems there are two varieties of heads for the Northstar... those with tappets where the cam is in direct contact with the tappet and those with rocker followers where the cam is actuating a follower with a roller tip. Can anyone explain the difference and which vehicles/variants of the northstar used which type of head configuration? I see a lot of confusion in the forums regarding the language and terminology. My Lucerne shop manual describes the heads as though I have rocker followers but when I pulled the valve covers my Northstar has tappets. With the tappet configuration there are no visible valve springs. Did someone do a motor swap on my Lucerne before I bought it or is the factory shop manual just wrong?

Is it a knocking or tapping noise, upper or lower in the engine. Those aren't cheap if they are not the problem. You can buy a cheap stethoscope from an auto parts store to help you pinpoint where the noise is coming from.

Looks like cam is offset to "outside" position so it is not directly over valve tip. So, are both cams on roller motors further apart than the cams on non-roller motors? Say, 4" on no roller motor and 5" on roller motor? Approx?

Re: Tappets or Rocker Followers - Two Different Head Designs???

Originally Posted by stoveguyy

Looks like cam is offset to "outside" position so it is not directly over valve tip. So, are both cams on roller motors further apart than the cams on non-roller motors? Say, 4" on no roller motor and 5" on roller motor? Approx?

Re: Tappets or Rocker Followers - Two Different Head Designs???

My Lucerne CXS is a 2006 that's why I'm confused. I think it would be really tough to swap the older motor into a 2006 because I have COP ignition and electronic throttle control. GM must have switched back to flat tappets for the LD8 Vin Y Lucerne and possibly the LD8 DTS? I would have expected it to have roller cam followers but instead it has flat tappets. The car is up at the dealership where I bought it. The technician swears up and down that the noise is valve train but it really sounds like a low end rod knock. The knock only occurs after the engine comes up to full operating temp after about 25 minutes of driving and then idles for about 5-10 minutes. After the knock fades in at idle it will get loud enough to hear from about 10 parking spots away. When I rev the motor I can hear the knock until about 2500 rpm before it just fades into the background with other noise. If I take the car out and drive it hard, the knock disappears until it sits idling for another 10 minutes or so and then it fades back in.

The engine is on the floor of the dealership and the tech has removed the rear cylinder head (closest to the fire wall.) When I stopped by yesterday I was able to feel the pistons and I admit I don't feel any play in the rods by pushing on the pistons. I suppose it's really hard to check out the condition of the rod bearings without taking the oil pan off.

Someone on Craigslist has a low mileage (25k) LD8 Vin Y northstar available for a 2008 DTS. If my aftermarket warranty dodges coverage and the dealer refuses to proceed I'm going to try to buy that engine and tell the dealer to just swap it out. I'll take the bad motor home to my garage and tinker with it while they stick the car back together. If I can prove the failure was an internal lubricated part then the aftermarket warranty is responsible for the repair.

The tech insisted he needed to pull the head to inspect the followers but I don't understand why. In any event, he didn't see any obvious problems. I don't even understand why he needed to drop the whole cradle to inspect followers. He should have just taken the valve covers off and performed the inspection in the vehicle. Now he claims he can't check tolerances in-house, he says the head needs to go to a machine shop to be inspected. I'm thinking he just doesn't know HOW to check tolerances and he pulled the head just because he isn't qualified to do the inspection himself. Either way, with the severity of the knock I would think it would have to be a fairly obvious major wear problem if it were valve train related.

When I stopped by the dealership yesterday I found the harmonic balancer in the parts pile and gave it a good look, I don't see any obvious cracking, it looks like the rubber is still in good shape and the bond looks fine. The flex plate is still hidden because the tech dropped the whole cradle with the trans still bolted to the engine. If I buy the used motor I'm going to make sure I get the flex plate and torque converter as well.

Re: Tappets or Rocker Followers - Two Different Head Designs???

The piston would have to be in the downstroke in order for you to feel play when you push on it. If it was in upstroke it has already pushed the play out of it.

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Did they even check the oil pressure?

Another thing to check could be torque converter bolts or even flexplate but the flexplate would require motor separation from tranny.
They may have opened that motor for no reason. A hairline crack on the flexplate around the bolt holes fits your description.

Re: Tappets or Rocker Followers - Two Different Head Designs???

If you can ever feel ANY play in a piston/connecting rod/crank bearing, you have BIG problems. The ONLY way to check rod bearing clearance is to use Plastigauge, and even then you're fooling with .0015" to .0025". (That's ten/thousandths of an inch) Sensitive fingertips ??? I don't think so.

Re: Tappets or Rocker Followers - Two Different Head Designs???

Generally the sensitive fingertips method exposes the culprit well enough when you are searching for a "nasty sounding knock that can be heard from 10 parking spaces away" (when clearances are not even close to spec), but I concur, it's not conclusive.

Re: Tappets or Rocker Followers - Two Different Head Designs???

I guaruntee the engine in my 2006 Lucerne CXS has flat tappets. It absolutely does not have rockers of any sort. There are no visible springs and the cam directly contacts the flat top of a tappet. I highly doubt it's the wrong engine because it uses COP ignition and electronic throttle control but I suppose someone might have swapped the heads... not sure if that's possible. If you heard the knocking sound you wouldn't need a micrometer to check rod bearings, but I understand what you're saying and you're right. I had all of about 3 minutes with the tech standing over my shoulder to just quickly touch each piston. I don't care what they do with it because at this point it's beyond the technical details. Unless it's something simple like a flex plate or torque converter bolt or an obviously stuck lifter I doubt anything other than engine replacement is going to get the problem solved.

I was just curious about these two different head designs, I'll dig a little further and see if I can find confirmation that Lucerne and DTS run flat tappets on the LD8 Vin Y. Perhaps they use rockers on the 300hp version?

Re: Tappets or Rocker Followers - Two Different Head Designs???

I guaruntee the engine in my 2006 Lucerne CXS has flat tappets. It absolutely does not have rockers of any sort.

Keep in mind that an overhead cam engine eliminates the need for rockers.

EDIT:
According to this diagram from GMpartsgiant, the engine appears to be the same as any other Northstar. Part #322 appears to be the roller follower and #323 the lash adjuster depicted in post #3 & 6. Something is wrong here, because GM is not going to make a Buick version of the Cadillac engine.

Re: Tappets or Rocker Followers - Two Different Head Designs???

Take another look at Ranger's parts blowup and the picture in Post #6 - those are NOT rocker arms; they are cam followers.

Cadillac went to roller cam followers in both the VIN 9 and VIN Y engines in 2000. I also find it "interesting" that the flat tappet follower was carried for another ?? 6 ?? years past 2000 ............